The present invention relates to a method of trimming the optical power and also reducing the distribution of optical power coupled from a semiconductor laser to an optical fiber or coupled to that part of a connector that is adapted to receive an optical fiber. This invention also relates to the resultant device.
When coupling light from a semiconductor laser into an optical fiber using either a bulk optic, microlens, graded index lens or the like, great variation of coupled power is observed from device to device. This may be the result of variations in laser output power, spot size, and far field pattern, as well as variations in lens throughput and laser-to-lens alignment. A system incorporating such devices must be able to operate with the range of powers that come from a distribution of devices.
In some applications, there is concern that too much light may be coupled into the fiber or, if the device is designed for use with removable fibers, that too much power may be emitted from the device when the fiber is not in place. The magnitude of acceptable powers coupled into a fiber or emitted from an unconnected device are set by national and international safety organizations. For maximum system performance, it is often important that the amount of power coupled into a fiber be as near the maximum acceptable value while not exceeding it. For a system designed to accept a number of devices, a narrow distribution of coupled powers is desirable since the system link budget is determined by the smallest coupled power within the distribution.
The amount of power emitted from the device cannot be reduced simply by decreasing the laser output power because modulated laser devices have a certain average power at which they must be operated for optimum modulation rate.
Nor is it acceptable to reduce the power coupled to a fiber by creating an angular or lateral deflection of the laser output beam axis with respect to the fiber axis so that the fiber core is no longer located at the maximum point on the laser power distribution curve. If this is done, relatively large changes of coupled power can occur in response to small misalignments which may occur as a result of welding or vibration during use, for example.